When processing synthetic resins, an intense mixing and degassing must often take place before the resin can be cast. This is particularly true for thermosetting casting resins and their components. The mixing often serves the further purpose of evenly distributing fillers in the synthetic resin. The viscosity of the mixture can typically vary within wide limits.
In the case of a mixer of the above-mentioned type, the speed of rotation of the worm conveyor must be sufficiently high that the container content is moved upwardly along the worm conveyor. In the case of relatively viscous mixtures, relatively low speeds of the worm conveyor are sufficient. The thinner the container content, the higher the rotational speed required of the worm conveyor in order to obtain the requisite conveying rate. When the agitating arms are fixedly connected to the worm conveyor, their speed corresponds with the speed of the worm conveyor. The agitating arms take the container content along in their direction of rotation, so that the container content is rotated.
A consequence of the rotation of the container content is that a surface is produced on the container content which is funnel-shaped. This surface differs more or less in shape from a paraboloid of revolution as a result of the friction at the container walls and due to the conveying of material by the worm conveyor. The thinner and less viscous the container content, the more distinct the resulting funnel-shaped distribution of the material, mainly due to the high speed of the agitating arms and also due to the relatively small friction within the material.
The funnel-shaped distribution is effected by centrifugal forces and can, at a low fill level, result in the worm conveyor no longer conveying any material upwardly, since its lower end is no longer sufficiently flooded. This can result, for small fill levels, in the material no longer being circulated across the discharge plate. As a help, mixers have been constructed which permit an uncoupling between the worm and agitating arms. After uncoupling, the agitating arms stand still, so that a funnel-shaped distribution no longer takes place. This makes it possible to circulate the material over the discharge plate, but at the expense of increased structural complexity, more complicated operation of the apparatus and the associated risk of operator errors, and possible degradation of the mixing after the agitating arms are uncoupled.
A basic purpose of the invention, therefore, is to construct an apparatus of the above-mentioned type which has rotating agitating arms and is capable of mixing small levels of fill satisfactorily and circulating the mixture over the discharge plate.